The present invention relates to a process for the production of rigid polyurethane foams having improved demold and outstanding insulation properties.
Processes for the production of rigid polyurethane foams are known. Sucrose-based polyols are of particular interest as the primary isocyanate-reactive reactant because of their relatively low cost, high functionality and because they are relatively simple to produce. Processes for producing such sucrose-based polyols are disclosed, for example, in U.S. Pat. Nos. 3,085,085; 3,153,002; 3,222,357; 4,430,490; and 5,539,006. Each of these patents teaches that sucrose-based polyols are useful in the production of polyurethane foams.
At the present time, a major concern of foam producers, particularly rigid foam producers, is the development of rigid foam systems in which the chlorofluorocarbon blowing agent is replaced with a more environmentally acceptable blowing agent. HCFCs (i.e., hydrogen containing chlorofluorocarbons), HFCs (hydrogen containing fluorocarbons), and hydrocarbons such as n-pentane cyclopentane, isopentane and blends of these blowing agents are presently considered to be possible alternatives.
Dishart et al's paper entitled “The DuPont Program on Fluorocarbon Alternative Blowing Agents for Polyurethane Foams”, Polyurethanes World Congress 1987, pages 59-66 discusses the investigation of various HCFCs as possible blowing agents for rigid polyurethane foams.
Various references have described the use of pentafluoropropanes as blowing agents in producing polyurethane foams. See, e.g., U.S. Pat. Nos. 5,496,866; 5,496,867; 5,426,127; 5,461,084; and 5,889,066.
Finally, several references have broadly suggested the use of sorbitol-based polyethers in producing polyurethane foams. See, e.g., U.S. Pat. Nos. 4,943,597; 5,798,533; 6,207,725; 6,284,812; 6,306,920; 6,339,110; 6,346,205; 6,380,275; and 6,433,032; and an article published in 2001 by Colvin, entitled “New Blowing Agents for Insulated Panels.” Of these references, U.S. Pat. Nos. 6,284,812; 6,306,920; and 6,380,275 and the Colvin article broadly suggest that sorbitol-based polyethers may be used with HFC-245fa.
A process in which for preparing a rigid foam having good physical properties, particularly good demold and insulating properties would, therefore, be advantageous. More particularly, it would be advantageous to produce a rigid foam from a pentafluoropropane blowing agent having lower freeze stable density at a lower overpack and improved k-factor and with other physical properties being at least equivalent to foams produced from sucrose-based polyethers.